Wireless communication systems are well known in the art. In such systems, communications (particularly voice communications) are typically supported by a wireless infrastructure that supports wireless communications with and between one or more wireless communication devices (or mobile devices), such as cellular phones, portable two-way radios, wirelessly-enabled personal digital assistants, etc. Increasingly, suppliers of such mobile devices are working toward the provision of more than just voice communications. For example, it is desirable to provide video information as well and, in particular, so-called multimedia information including coordinated audio and video.
In general, audio/video multimedia content comprises audio information and video information streams that are independently encoded and multiplexed onto a single composite data stream. At a decoding device, the composite data stream is de-multiplexed and the resulting encoded audio and video streams are separately decoded. The respective audio and video decoding processes must be synchronized such that one process does not get too far ahead (in a temporal sense) of the other. Otherwise, the resulting presentation of decoded audio and video information may be objectionable where, for example, the decoded audio information of a speaker does not match the movement of the speaker's lips depicted in the decoded video information. This lack of synchronization is a significant problem, particularly in light of the fact that current audio and video encoding techniques typically do not provide encoded output at the same rate, i.e., they have different frame rates. This is further exacerbated by video encoders that do not operate at a strict frame rate and, instead, operate in a quasi-periodic fashion.
One class of technique addresses this synchronization problem by synchronizing the audio and video decoding processes to a high-resolution system timer reference. While these techniques work, they are not particularly attractive for use in mobile devices in which power consumption is always a concern. That is, the need to implement a system timer that is always available necessarily leads to decreased battery life in mobile devices.
In an alternative technique, the delay incurred by video decoding is continuously determined, which delay is thereafter used to adjust a variable delay to be induced in the audio decoding process. In essence, the decoding of audio information is slaved to the decoding of the video information by purposefully delaying audio decoding to match video decoding. However, this technique requires the provision of relatively sophisticated circuitry or processing to first determine the delay resulting from the video decoding process and to thereafter apply the delay in a variable fashion to the audio decoding process. Again, such circuitry or processing would prohibitively consume power resources in mobile devices.
Therefore, a need exists for a technique that facilitates synchronization of decoded audio and video information, particularly in mobile devices where minimized power consumption is essential.